Error in MultiOutputClassifier: Number of classes must be greater than one

What will you learn?

In this tutorial, you will master the art of fixing the error “The number of classes has to be greater than one; got 1 class” that often arises when utilizing the MultiOutputClassifier from scikit-learn. By understanding why this error occurs and how to rectify it, you will enhance your skills in multi-class classification.

Introduction to the Problem and Solution

Encountering an error message stating that the number of classes should exceed one while having only a single class is a common issue when working with multi-output classifiers in scikit-learn. To tackle this challenge effectively, it is essential to ensure that your dataset comprises multiple unique classes for accurate classification.

To address this problem: 1. Inspect your data and labels to verify the presence of multiple distinct classes. 2. Modify your dataset or adjust parameters within the MultiOutputClassifier constructor if needed. 3. Seek personalized assistance at for tailored solutions.


# Your solution code here
from sklearn.multioutput import MultiOutputClassifier

# Check data and labels for multiple unique classes
# Ensure target variable contains more than one distinct class

# Resolve any issues causing the single-class error

# Adjust parameters like 'n_classes' in MultiOutputClassifier constructor if required

# For customized support, visit 

# Copyright PHD


The error “The number of classes has to be greater than one; got 1 class” occurs due to MultiOutputClassifier expecting multiple unique classes for classification tasks. Here’s a breakdown:

  • Data Inspection: Examine your dataset to confirm the presence of diverse classes in the target variable.

  • Resolution Steps: Rectify the issue by introducing varied classes into your dataset or tweaking relevant parameters within MultiOutputClassifier.

By following these steps, you can eliminate the error and progress seamlessly with multi-class classification using MultiOutputClassifier.

    Why am I encountering this error message?

    This error surfaces when MultiOutputClassifier detects only a single unique class in your dataset meant for classification.

    How can I determine if my data exhibits multiple unique classes?

    Utilize tools like NumPy or pandas in Python to analyze your target variable and identify distinct class instances.

    Can adjusting hyperparameters aid in resolving this issue?

    Yes, modifying parameters such as ‘n_classes’ within MultiOutputClassifier can sometimes mitigate such errors.

    What should I do if my data indeed comprises only one class?

    Revisit your data preparation process if your dataset genuinely contains just one class due to oversight or preprocessing steps before proceeding with modeling.

    Are there alternative classifiers available for multi-output scenarios?

    Apart from MultiOutputClassifier, scikit-learn offers ensemble methods like RandomForest capable of handling multi-output tasks effectively.

    Does feature engineering influence fixing this issue directly?

    While feature engineering may not directly impact resolving single-class errors, it can enhance overall model performance significantly.

    How does cross-validation help address such errors?

    Cross-validation techniques assist in validating model performance across different folds and identifying issues like imbalanced datasets leading to single-class situations.

    Is automating detection of single-class occurrences feasible?

    You can create custom functions using Python libraries like NumPy or pandas to automatically detect instances where datasets exhibit only one unique label/class value.


    Mastering resolution techniques for errors related to insufficient distinct classes is pivotal when working on classification tasks with scikit-learn’s MultiOuputClassifer. By ensuring proper dataset handling and parameter adjustments as needed, you can efficiently overcome such obstacles and elevate your machine learning proficiency.

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